The present invention generally pertains to data transfer systems and is particularly directed to a method and system for monitoring transfer systems having serially distributed data ports.
More specifically, the present invention provides a method and system for monitoring the type of data transfer system described in U.S. patent application No. 428,545 by Herbert Alan Schwan filed Sept. 21, 1982 for "Telemetry System for Distributed Equipment Controls and Equipment Monitors." In the data transfer system described in the Schwan patent application, data ports are connected in series to a receiver by an input data line for serial transmission of input data to the receiver over the input data line; and data ports are connected in series to a transmitter by an output data line for serial transmission of output data from the transmitter over the output data line. A clock line provides a clock signal to the data ports for common system timing. In such system, the output and/or input data ports are connected by the respective output and/or input data line serially as a chain of shift register stages. A frame of output data from the transmitter is shifted down the output data line with each shift being clocked by a clock pulse, until the beginning of the data frame reaches the last shift register stage (data port) in the chain. At that time a frame pulse simultaneously enables all of the shift register stages (data ports) to transfer the instant data from the output data line for further transfer to output devices connected to the respective data ports. A frame of input data is shifted serially up the input data line to the receiver in the same manner from data ports that are connected to each other in series to function as stages of a shift register. This type of system is referred to herein as a Schwan system.
The input data ports are individually connected to different input devices, such as equipment monitors, for transferring input data onto the input data line from the respective input devices; and the output data ports are individually connected to different output devices, such as equipment controls for transferring output data to the respective output devices from the output data line.
The term "data port" should not be interpreted as necessarily implying a data module. Several data ports may be connected serially as shift register stages within a single data module which is connected to an input or output device to transfer the data through the several data ports from or to several terminals in the input or output device respectively. In this regard, each terminal in the input or output device is considered to be coupled to a separate input or output device.
Improved Schwan systems are described in U.S. patent application No. 561,567 by Anthony E. Diamond filed Dec. 15, 1983 for "Addressable Port Telemetry System" and in U.S. patent application No. 622,984 by Anthony E. Diamond filed June 21, 1984 for "Addressable-Port, Daisy Chain Telemetry System with Self-Test Capability." The systems described in the Diamond patent applications include an address circuit at each port for determining when that port is enabled to transfer data signals onto or from the data line independent of the port's physical location on the data line.
U.S. patent application No. 622,984 by Diamond describes an input/output daisy chain data transfer system which includes a subsystem for determining the serial location of a data port where a failure has occurred. In such data transfer system, the input data line and the output data line each serially connect the input data ports and the output data ports; and the subsystem for determining the location of a failure includes a circuit for generating a predetermined test control signal during first-state intervals of the clock signal and for generating predetermined test data signals during immediately following second-state intervals of the clock signal. The transmitter is coupled to the test signal generator for transmitting the test control and test data signals over the output data line. This subsystem further includes a circuit in each data port for recognizing the test control signal and for responding to such recognition by transferring the immediately following test data signal from the output data line onto the input data line in substitution for the input data signal, whereby the test data signal is carried to the receiver; a comparator for comparing the data signal received by the receiver over the input data line with the test data signal; and a counter for counting clock signal pulses beginning upon the transmission of the test data signal and continuing until a data signal is received over the input line that is different than the test data signal that was transmitted over the output line to thereby obtain a count indicating the number of data ports removed from the transmitted at which a data port failed to accurately return the test data signal that was transmitted.
It also is desirable to be able to monitor a Schwan data transfer system to determine the number of data ports connected in the input data line and in the output data line respectively and to determine whether there has been a change in the respective numbers of such ports between times of operation of the system.